Aqueous HClO4 Research Articles

In situ scanning tunneling microscopy study of adsorption of diaza-15-crown-5 on Cu(1 1 1)

Adsorption of diaza-15-crown-5 (1,4,10-Trioxa-7,13-diazacyclopentadecane: C 10H 22N 2O 3) on Cu(1 1 1) in aqueous HClO 4 solution has been investigated using cyclic voltammetry and in situ electrochemical scanning tunneling microscopy (STM). Diaza-15-crown-5 molecules form a well-ordered adlayer. A Cu(1 1 1)-(4×4) structure for the molecular array is determined. A proposed model is used to explain the molecular registry with the substrate.

Kinetics of oxidation of acidic amino acids by sodium N-bromobenzenesulphonamide in acid medium: A mechanistic approach

Kinetics of oxidation of acidic amino acids (glutamic acid (Glu) and aspartic acid (Asp)) by sodium N-bromobenzenesulphonamide (bromamine-B or BAB) has been carried out in aqueous HClO4 medium at 30°C. The rate shows first-order dependence each on [BAB]o and [amino acid]o and inverse first-order on [H+]. At [H+] > 0·60 mol dm−3, the rate levelled off indicating zero-order dependence on [H+] and, under these conditions, the rate has fractional order dependence on [amino acid]. Succinic and malonic acids have been identified as the products. Variation of ionic strength and addition of the reaction product benzenesulphonamide or halide ions had no significant effect on the reaction rate. There is positive effect of dielectric constant of the solvent. Proton inventory studies in H2O-D2O mixtures showed the involvement of a single exchangeable proton of the OH− ion in the transition state. Kinetic investigations have revealed that the order of reactivity is Asp > Glu. The rate laws proposed and derived in agreement with experimental results are discussed.

Thermodynamic Properties of Aqueous HClO4 to 373 K and at Low Pressure: A Comprehensive Pitzer Ion-Interaction Model

We present a Pitzer ion-interaction model fit to most of the available isopiestic, dilution enthalpy, heat capacity, and volumetric data for HClO4(aq). Osmotic and activity coefficients are accurately reproduced for molalities between infinite dilution and 8 mol kg-1 at 298 K. Isopiestic data at temperatures other than 298 K do not appear to be reliable. The dilution enthalpy data at 298 K are also reproducible to 8 mol kg-1; consequently, HClO4(aq) activities may be calculated to 8 mol kg-1 at 298 K and at somewhat higher or lower temperatures with only minor losses in confidence. Heat capacity data do not extend beyond 1.7 mol kg-1 at 298 K and 1.0 mol kg-1 at T > 328 K, and interlaboratory agreement is poor. Consequently, activity coefficients and thermal properties may only be calculated to about 1 mol kg-1 at 373 K. There are numerous volumetric data for molalities between 0.02 and 18 mol kg-1 and at 298 K; however, there are large variances between datasets at m > 5 mol kg-1. Volumetric data at T > 348 K are limited to one study and m < 1 mol kg-1. The volumetric form of the model is simple but due to disagreement between datasets is considered to have large uncertainties.

Preparation, structures and reactions of isomeric [Co(cyclen)(O2C2O2)]+ and [Co(cyclen)(O2CCH2CO2)]+ complexes (cyclen = 1,4,7,10-tetraazacyclododecane) †

The syn,anti and syn,syn forms of the complexes [Co(cyclen)(O2C2O2)]ClO41 and 2 respectively and [Co(cyclen)(O2CCH2CO2)][ClO4]·H2O 3 and 4 respectively (cyclen = 1,4,7,10-tetraazacyclododecane) have been prepared and their single crystal structures determined. Protonated forms of 3 and 4 are obtained as their ClO4− salts on crystallisation of the parent complexes from aqueous HClO4, and a crystal structure of the former shows protonation occurs on a carbonyl O atom in the malonato bidentate ligand. Proton exchange (D2O, 25.0 °C, I = 1.0 M) of the equatorial NH protons (syn and anti) in 1, 2, 3 and 4 is first order in [OD−], with kH values in the range (1–8) × 107 M−1 s−1. Equilibration between the syn,anti and syn,syn forms of the complexes follows the rate equation kobs = kisom[OH−] with kisom = (1.3 ± 0.1) × 105 M−1 s−1 (25.0 °C, I = 1.0 M NaCl) for both systems, and with final equilibrium distributions of [2]/[1] = 0.100 ± 0.005 and [4]/[3] = 0.057 ± 0.002. The various equatorial NH sites are very susceptible to inversion, with rate constants for lone pair inversion of the deprotonated centres being in the range 2 × 106 to 1 × 108 s−1 at 25 °C. Alkaline hydrolysis (25.0 °C, 1.0 M, NaClO4) of [Co(cyclen)(O2CCH2CO2)]+ gives [Co(cyclen)(OH)2]+ in a biphasic reaction, with both paths first order in [OH−], kOH(1) = 26.9 ± 0.6 M−1 s−1, kOH(2) = 4.9 ± 0.6 M−1 s−1, whereas alkaline hydrolysis of [Co(cyclen)(O2C2O2)]+ gives [Co(cyclen)(OH)2]+ in one step, kOH = 0.114 ± 0.009 M−1 s−1. Mechanisms for the reactions are discussed.

Micellar effect on the reaction of picolinic acid catalyzed chromium(VI) oxidation of dimethyl sulfoxide in aqueous acidic media: A kinetic study

The kinetics and mechanism of picolinic acid (PA) catalyzed oxidation of dimethyl sulfoxide (DMSO) to dimethyl sulfone by chromium(VI) in both aqueous H2SO4 and HClO4 media have been studied in the absence and presence of surfactants at different temperatures. Cr(VI)–PA complex formed in preequilibrium steps is the active oxidant that experiences the nucleophilic attack by DMSO to form a positively charged intermediate ternary complex. Within the proposed ternary complex, an oxygen transfer or a ligand coupling or both occurs to generate the product, dimethyl sulfone. Cr(VI) is ultimately converted to Cr(III)–PA complex. Under the experimental conditions, the process shows a first-order dependence on each of the reactants (i.e., [Cr(VI)]T, [PA]T, [DMSO]T, and [H+]). HCrO4− has been found kinetically active. The reaction is catalyzed by sodium dodecyl sulfate (SDS, a representative anionic surfactant) monotonically, while cetylpyridinium chloride (CPC, a representative cationic surfactant) retards the reaction continuously. The observed micellar effects have been explained by considering the hydrophobic and electrostatic interaction between the surfactants and reactants. A pseudo-phase ion exchange (PIE) model has been applied to explain the micellar effect. The Piszkiewicz cooperative model has been applied to determine the kinetic parameters, and it indicates the existence of catalytically productive submicellar aggregates. Because of this reactant-promoted micellization of the surfactant before or below the cmc value, the present systems do not show any discontinuity at the respective reported cmc values of the surfactants. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 173–181, 2001

Formation of Excited Uranyl in U(IV) Oxidation with Oxygen in Aqueous HClO4 Solutions: III. Effects of Deuteration of Solvents and Heterogeneous Decay of Radicals

The surface of the glass introduced in the form of spheres with R = 1 mm into Teflon reactor affects both the kinetics of the liquid-phase chemiluminescent chain-radical oxidation of U(IV) with oxygen and the efficiency of conversion of the chemical reaction energy into the light energy. In the case of deuterated solutions, the reaction deceleration and the decrease in the chemiluminescence efficiency in the presence of the glass were less pronounced. A mechanism of the chemiluminescent reaction was considered which assigns an important role to heterogeneous decay of OH and HO2 (OD and DO2) radicals.

Electrochemical synthesis and structural and physical characterization of one- and two-electron-reduced forms of [SMo12O40]2-.

Isolation of a soluble [NHex4]+ salt has allowed a detailed electrochemical study of the anion alpha-[SMo12O40]2- to be undertaken. Four reversible one-electron-reduction processes are observed in CH2Cl2 solution. Controlled potential electrolysis led to isolation of tetraalkylammonium salts of the one-electron-reduced anion alpha-[SMo12O40]3- and the two-electron-reduced anion alpha-[SMo12O40].4- [SMo12O40]3- is stable to disproportionation in dry solvents (Kdis = 10(-7.4). EPR and magnetic susceptibility data indicate that [SMo12O40]3- is a simple paramagnet (S = 1/2) while [SMo12O40]4- is paramagnetic with the mu eff values decreasing at low temperatures. Solutions of the two-electron-reduced species are EPR silent, but microcrystalline powders show very weak signals. The crystal structure of alpha-[NBu4]3[SMo12O40] has been determined (triclinic P1; a = 13.840(3) A; b = 15.587(4) A; c = 19.370(3) A; alpha = 94.82(2) degrees; beta = 93.10(1) degrees; gamma = 91.05(2) degrees; Z = 2). There is disorder around the C2 axis of the central SO4(2-) tetrahedron. In the presence of aqueous HClO4 (0.045 M) in thf/H2O or MeCN/H2O (98/2 v/v), [SMo12O40]2- exhibits five two-electron-reduction processes. Under these conditions, [SMo12O40]3- protonates and disproportionates into [SMo12O40]2- and the (2e-, 2H+)-reduced anion [H2SMo12O40]2-.

Kinetics of hydrogen evolution on single crystal bismuth electrodes

Hydrogen evolution reaction on Bi(001) and Bi(111) faces from aqueous HClO4 and acidic LiClO4 solutions are studied. The applicability of the Frumkin theory of slow discharge is tested. The transfer coefficients corrected for the diffuse double layer are found. The hydrogen evolution overpotential is higher for less active basal Bi(111) face, explained by the lower specific adsorption energy of H2O molecules on Bi(111) than on more active Bi(001) face.

Uranyl-catalyzed chemiluminescent reaction of U4+ oxidation by dioxygen in aqueous HClO4 solution

Chemiluminescence (CL) accompanying the reaction of U4+ with O2 in 0.0004–0.1M HClO4 was studied. It was found that the electron-excited uranyl ion (UO22+)* is the CL emitter. The fact that the reaction rate and the CL yield increase as the solution acidity decreases was explained by different reactivities of the Uaq4+ aquation and the products of its stepwise hydrolysis, UOH3+ and U(OH)22+, toward O2. Based on the results of analysis of the chain-radical mechanism of the reaction between U4+ and O2, it was concluded that transfer of an electron from the UO2+ ion to the oxidizing agent (a ·OH radical) is the most plausible elementary step of the reaction of (UO22+)* formation. It was found that the reaction rate, as well as the CL yield, increase substantially in the presence of uranyl ion. Catalytic action of UO22+ was explained by the formation of a UO22+·UO2+ complex, which reduces the rate of the UO2+ disproportionation reaction (UO2+ is an intermediate of the reaction and is involved in chain propagation), and by regeneration of the active center, UO2+, in the reaction of UO22+ with U4+.

Chronoamperometric resolution of ion and solvent transfers at a poly( o-toluidine) modified electrode by combined electrochemical quartz crystal microbalance (EQCM) and probe beam deflection (PBD)

Combined electrochemical quartz crystal microbalance (EQCM) and probe beam deflection (PBD) measurements on short time scales following the application of a potential step are presented. The procedure for evaluating the exchange of mobile species (ions and solvent) is illustrated by application of the combined technique to a poly( o-toluidine) (POT) film redox switching in aqueous HClO 4 solutions. A comparison of the predicted PBD profiles calculated from the current and mass responses to that of the measured PBD signal, by temporal convolution analysis, enabled the contributions of anion (ClO 4 −) and solvent (H 2O) transfer at the first redox step to be discriminated quantitatively. The results are consistent with a mechanism where anion exchange involves a counter flux of solvent, and suggest that a film volume constraint is applicable on the time scale of the experiment. During oxidation and reduction, the EQCM indicates a non-equilibrium movement of anions, confirmed by convolution analysis of the associated current and deflection signals.

Electrocatalysis in photochemically activated electropolymerized thin films.

In reductively electropolymerized thin films of poly-cis-[Ru(vbpy)2(py)2](PF6)2 ("vbpy" is 4-methyl-4'-vinyl-2,2'-bipyridine and "py" is pyridine), on glassy carbon electrodes, photochemical ligand loss with aqueous HClO4 in the external solution occurs to give poly-cis-[Ru(vbpy)2(OH2)2](ClO4)2, but the efficiency of ligand loss is greatly decreased compared to the efficiency in solution. In cyclic voltammograms of films containing the aqua complex, there is evidence for both RuIII/II and higher oxidation state RuIV/III, RuV/IV, and RuVI/V couples. The redox chemistry of the resulting films is dictated by the film structure and can be controlled by varying the electropolymerization conditions and external solution composition. The oxidation of alcohols by these higher oxidation state couples has been investigated electrochemically.

Stepwise Complexation of Ni(II) and Cu(II) Ions by 6,6‘-C-spirobi(cyclam) (cyclam = 1,4,8,11-Tetraazacyclotetradecane), L1. Syntheses and Redox Chemistry of [M(H2L1)]X4(M = Cu2+, Ni2+), [Cu2(L1)]X4, and [CuNi(L1)]X4(X = ClO4-) and the X-ray Crystal Structure of [Cu2(L1)](ClO4)4

In aqueous HClO(4), the cation [H(4)(L(1))](4+) where L(1) is 6,6'-C-spirobi(cyclam) (cyclam = 1,4,8,11-tetraazacyclotetradecane), complexes Cu(2+) and Ni(2+) ions in a stepwise fashion to form [M(H(2)L(1))](ClO(4))(4) (M = Cu(2+) and Ni(2+)) from which [CuNi(L(1))](ClO(4))(4) has been prepared selectively. The preparation and the structure of [Cu(2)(L(1))](ClO(4))(4) (empirical formula, C(19)H(44)N(8)Cu(2)Cl(4)O(16); space group, triclinic; P&onemacr;; a = 8.1815(6) Å, b = 12.6098(9) Å, c = 16.6565(12) Å, alpha = 80.3890(10) degrees, beta = 76.5840(10) degrees, gamma = 87.1750(10) degrees, V = 1647.9(2) Å(3), and Z = 2; of the 9531 total reflections collected, 6779 reflections with I > 2sigma(I) on least-squares refinement provided final R(1) = 0.0657 and wR(2) = 0.1424) are also reported. The cyclic voltammograms (1.0 M NaCl, 0.1 M H(+); Pt electrodes; all E(1/2) vs NHE) of [M(H(2)L(1))](4+) (M = Cu(2+) and Ni(2+)) ions show single waves for the Cu(II)/Cu(III) couple (E(1/2) = 0.79 V, irreversible) and the Ni(II)/Ni(III) couple (E(1/2) = 0.56 V, reversible), respectively. In CH(3)CN (0.1 M Et(4)NClO(4)), the [Cu(2)(L(1))](4+) ion shows a reversible wave for the Cu(II)-Cu(II)/Cu(II)-Cu(III) couple ((1)E(1/2) = 1.120 V) and an irreversible wave for the Cu(II)-Cu(III)/Cu(III)-Cu(III) couple ((2)E(1/2) = 1.430 V). Similarly, a reversible wave for the Cu(II)-Ni(II)/Cu(II) -Ni(III) couple ((1)E(1/2) = 0.750 V) and an irreversible wave for the Ni(III)-Cu(II)/Ni(III)-Cu(III) couple ((2)E(1/2) = 1.20 V) are observed in the case of the [Cu(II)Ni(II)(L(1))](4+) ion. The [Cu(2)(L(1))](4+) ion (g( perpendicular) = 2.120, g( parallel) = 2.256 and 2.196, A( parallel) = 150 G, and D( parallel) = 75 G) and the mixed valent species [Cu(II)Ni(III)(L(1))](5+) (for Cu(2+), g( perpendicular) = 2.060, g( parallel) = 2.219, and A( parallel) = 100 G; for Ni(3+) in sulfate media, g( perpendicular) = 2.204 and g( parallel) = 1.967) and [Cu(II)Cu(III)(L(1))](5+) (g(xx)() = 1.982, g(yy)() = 2.155, g(zz)() = 2.386, A(yy)() = 80 G, and A(zz)() = 120 G) show dipolar-dipolar interaction. In the mixed-valent ions, due to strong electrostatic repulsion from either the Ni(III) or Cu(III) ions, significantly smaller A( parallel) (or A(zz)()) values are observed for the Cu(2+) ion compared to 200 G in the mononuclear ions. Also, the [Cu(II)Ni(II)(L(1))](4+) in aqueous HClO(4) and the [Ni(2)(L(1))](4+) ion in CH(3)NO(2) show a tendency to reduce perchlorate very slowly.

In Situ Scanning Tunneling Microscopy of Highly Ordered Adlayers of Aromatic Molecules on Well-Defined Pt(111) Electrodes in Solution: Benzoic Acid, Terephthalic Acid, and Pyrazine

In situ scanning tunneling microscopy (STM) was employed to study adlayer structures of benzoic acid, terephthalic acid, and pyrazine at a well-defined Pt(111) electrode in an aqueous HClO4 solution. Although benzoic acid formed disordered structures on Pt(111), high-resolution STM imaging was able to distinguish between the aromatic ring and two oxygen atoms of each flat lying benzoic acid molecule. Terephthalic acid formed a highly ordered adlayer with c(2√3 × 4)rect symmetry. Two carboxylic acid functional groups at the para-position were clearly discerned. Intermolecular interactions, presumably through hydrogen bonding, played an important role in the formation of the ordered adlayer. Pyrazine molecules formed an ordered adlayer at a relatively negative potential of 0.2 V vs a reversible hydrogen electrode. It was assumed that the molecules adsorbed horizontally at 3-fold hollow sites, forming a long range ordered adlattice of (√7 x √7)R19.1°. Disordered structures were found when the electrode poten...

Ethanol oxidation on PtRu electrodes studied by differential electrochemical mass spectrometry

Abstract The oxidation of ethanol in aqueous HClO 4 was studied on co-electrodeposited PtRu electrodes in a temperature range of 5–40°C by means of differential electrochemical mass spectrometry (DEMS). The formation of carbon dioxide and acetaldehyde were monitored by ion currents at appropriate masses. The presence of Ru promotes the surface reaction between the organic chemisorbate and the oxidant, whereas it may inhibit ethanol adsorption on the electrode. Optimum composition of the electrode for total oxidation was found to vary from Pt 0.67 Ru 0.33 at 5°C to Pt 0.85 Ru 0.15 at higher temperatures.

In Situ Scanning Tunneling Microscopy of Well-Defined Ir(111) Surface: High-Resolution Imaging of Adsorbed Sulfate

It is demonstrated by using in situ scanning tunneling microscopy (STM) that well-defined Ir(111) surfaces can be exposed in aqueous solutions by a flame-annealing−quenching technique. Atomically flat terrace-step structures were consistently observed in the double layer potential range in an aqueous HClO4 solution. It is shown that sulfate/bisulfate anions form highly ordered adlayers on Ir(111) in H2SO4 solution over a wide potential range. In situ STM images disclosed an Ir(111)−(√3 × √7) structure, which is identical with that found previously on Au(111), Pt(111), Rh(111), and Cu(111). High-resolution STM imaging allowed us to determine the orientation of hydrogen-bonded water molecules. Two different water molecules were clearly distinguished as separate spots along the √3 direction between neighboring rows of adsorbed sulfate.

Styrene hydration and stilbene isomerization in strong acid media. An excess acidity analysis

Rate constants obtained for the hydration of some ring-substituted styrenes, YC6H4CR=CH2 (R = H, CH3, CF3) (1-3), and for the isomerization of some cis-stilbenes substituted in both rings, YC6H4CH=CHC6H4Z (4), in aqueous H2SO4, D2SO4, and HClO4 media at 25°C and, in some cases, at other temperatures, have been subjected to an excess acidity analysis. Data obtained by different groups and in different media for the same substrates agree very well. The m‡ values obtained show that all the substrates react via the A-SE2 mechanism, rate-determining proton transfer to carbon; the transition state is late, with the proton transfer being about three-quarters complete. The reactivities of 1-3 in the aqueous standard state are obtained by extrapolation; they are 1:103:10-7, respectively. The stilbenes are relatively unreactive; log k0 values for compounds with substituents in the ring adjacent to the developing positive charge show a good correlation with σ+ with a large negative ρ+ value, but those for compounds with substituents in the other ring correlate with σ with a small negative ρ. Extrapolated log k0 values for 1 and 3 show a good correlation with σ+, but those for 2 correlate with neither σ+ nor σ, because the α-CH3 group twists the molecule and reduces the resonance interaction of ring substituents with the developing positive charge. On the other hand, this effect is not seen in 3, when the strongly deactivating α-CF3 group is present, meaning that the transition state is forced to be planar in this case. The activation parameters, solvent isotope effects, and excess acidity slope parameters m‡m* obtained in the analysis are tabulated and discussed. The parameters obtained for the parent styrenes 1 are very similar to those previously obtained for the phenylacetylenes YC6H4Ctriple bondCH, meaning that reactions with vinyl cation intermediates and reactions with benzyl cation intermediates can be quite similar. Key words: styrenes, stilbenes, hydration, excess acidity, LFER, mechanism.

In Situ Observation of Electrochemical Formation and Degradation Processes of Polyaniline by Fourier-Transform Infrared Spectroscopy

The electrochemical polymerization of aniline on a platinum electrode in aqueous HClO4 and H2SO4 solutions has been studied by means of in situ Fourier-transform infrared (FTIR) reflection spectroscopy. The spectra, taken at early stage of the polymerization in both solutions, exhibited the absorption characteristic of polyaniline (PAn) in an emeraldine state, even at a highly positive potential (≥+0.7 V vs. Ag/AgCl (saturated KCl)). Polymer growth in H2SO4 was accompanied by an increase in the molar ratio of [HSO4-]/[SO42-], indicating that the protons generated during the oxidation of aniline react with SO42- to afford HSO4-, and that polymer growth is facilitated. In contrast, such proton-scavenging behavior was not observed in a HClO4 solution, and the growth of PAn was suppressed owing to the accumulation of protons. Under the condition that aniline was extremely consumed, the produced PAn was subjected to oxidative degradation, which was competitive with the growth process of PAn. The major degradation species was identified to be p-benzoquinone.

2(5H)-furanone in the vilsmeier—haak reaction. Synthesis of β-substituted furans. Molecular structures of 3-dimethylaminomethylene-5-formyl-2(3H)-furanone and dimethylammonium 3,5-di(2,2-dimethyl-4,6-dioxo-1,3-dioxan-5-ylidenemethyl)-2-furanolate

The reaction of 2(5H)-furanone with the Vilsmeier-Haak-Arnold reagent and subsequent addition of concentrated aqueous HClO4 to the reaction mixture give (3-dimethylaminomethylen-2-oxo-3H-5-furanyl)methylenimmonium perchlorate, whose hydrolysis under various conditions leads to 3-dimethylaminomethylene-5-formyl-2(3H)-furanone or to the potassium salt of 5-hydroxy-2,4-furandicarbaldehyde. The reaction of these products with CH-acids was studied. The structures of the key compounds of this work have been proved by the method of X-ray diffraction analysis.

Kinetics and Mechanism of the Chromium(VI) Oxidation of Formic Acid in the Presence of Picolinic Acid and in the Presence and Absence of Surfactants

The kinetics and mechanism of picolinic acid (PA)- catalysed oxidation of formic acid have been studied in aqueous HClO4 media under the experimental conditions, 103[Cr(VI)]T = 0.67-2.67 mol dm-3, [PA]T = 0.01-0.12 mol dm-3, [HCO2H]T = 0.1-0.8 mol dm-3, [H+] = 0.35-1.5 mol dm-3,1 = 1.5 mol dm-3 in the temperature range 25-40° C. The kinetic parameters of the catalysed path have been compared with those of the relatively slower uncatalysed path which proceed parallelly with the catalysed path. In the catalysed path, Cr(VI)-PA cyclic complex formed at the pre-equilibrium step receives a nucleophilic attack at the Cr(VI) centre by the substrate leading to a ternary complex with the release of a proton in a reversible path. Then the ternary complex experiences the redox decomposition at the rate-determining step giving rise to Cr(IV)-PA complex and CO2. Then the Cr(IV)-PA complex reacts faster ultimately giving rise to Cr(III)-PA complex. The anionic surfactant sodium dodecyl sulfate (SDS) catalyses both the uncatalysed and catalysed paths in aqueous HClO4 media while the cationic surfactant cetyl pyridinium chloride (CPC) inhibits the reactions in aqueous H2SO4 media. In the presence of the surfactants, applicability of the Piszkiewicz model has been tested for the ΡΑ-catalysed path. Micellar effects are in conformity with the proposed mechanism.

A voltammetric investigation of the reactions between surface-confined amines and quinones on gold electrodes: evidence for imine formation

Abstract A surface-confined layer containing naphthoquinone was prepared by reacting 2,3-dichloronaphthoquinone with the amino tail groups of an aminoethanethiolate-modified vapor-deposited gold surface; this surface layer was then reacted with β -ferrocenylethylamine. These modified gold electrodes were examined with cyclic staircase voltammetry in aqueous HClO 4 at the completion of each step in this sequence of reactions. The voltammetric signature for the 2e − , 2H + reduction of the quinoid redox centers disappeared after the ferrocene compound was reacted with the naphthoquinone surface layer; furthermore, the surface coverage of ferrocene was twice that expected on the basis of a 1:1 reaction between the surface-bound naphthoquinone and β -ferrocenylethylamine. These results suggest that the latter reacts with the naphthoquinone carbonyl groups to form a surface-confined di-imine, which cannot be reduced within the electrochemical potential window of aqueous HClO 4 . In similar experiments, 2-[4′-( β -ferrocenylethylaminocarbonyl)phenyl]-1,4-naphthoquinone and 2-[2′-( β -ferrocenylethylaminocarbonyl)ethyl]anthraquinone were synthesized and reacted with aminoethanethiolate-modified gold surfaces. When examined at a platinum electrode in nonaqueous solvents, both of the freely diffusing compounds exhibited two pairs of voltammetric waves characteristic of quinoid and ferrocene functionalities. However, only the ferrocene redox centers of the resulting surface-confined layers were electroactive, suggesting that the reaction of these compounds with the surface-confined aminoethanethiolate involves conversion of the quinoid carbonyls to imines.